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weak interactions

This article explores the development of the weak interactions and the electroweak theory, from Enrico Fermi's work in 1936 to the discovery of the Higgs boson. It discusses the gauge theory of the electroweak interactions proposed by Glashow, Salam, and Weinberg, and the concept of spontaneous symmetry breaking. The article also examines the prediction and measurement of the masses of the weak bosons and the problem of mass generation in the electroweak theory.

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weak interactions

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  1. weak interactions

  2. weakdecays betadecay of neutron

  3. e p n neutrino direct interaction of four fermions Enrico Fermi, ~1936

  4. Enrico Fermil

  5. 1964 ===> gauge theory electroweak

  6. 1957 weak bosons W J. Schwinger

  7. - 1964 - 1968 gauge theory of the electroweak interactions ( Glashow, Salam, Weinberg )

  8. Glashow Salam Weinberg 1964-1968

  9. weak and electromagnetic interactions partial unification

  10. gaugegroup SU(2)xU(1)

  11. S U (2) x U (1) weak interaction electromagnetic interaction

  12. SU(2) x U(1) 3 + 1 gauge bosons photon Z W(+) W(-)

  13. SU(2)xU(1) weak interactions electromagnetism neutral current

  14. SU(2)xU(1) neutral current CERN 1972

  15. photon: superposition of SU(2) and U(1) – gauge boson Why photon massless? Why W – boson massive?

  16. mass generation by spontaneous symmetry breaking ( “ Higgs “ – mechanism)

  17. Minimal electroweak theory Gauge group: SU(2) x U(1)

  18. SU(2) U(1) fermions

  19. symmetry breaking: SU(2) and U(1) are broken, but the electric charge is unbroken

  20. neutral current interaction parity violation

  21. neutral current interaction parity violation observed in atomic physics

  22. weak interactions

  23. weakdecays betadecay of neutron

  24. e p n neutrino direct interaction of four fermions Enrico Fermi, ~1936

  25. Minimal electroweak theory Gauge group: SU(2) x U(1)

  26. symmetry breaking: SU(2) and U(1) are broken, but the electric charge is unbroken

  27. M(W) = 80.4 GeV M(Z)= 91.2 GeV CERN, 1984 =>

  28. The massesoftheweakbosonsarepredicted, oncetheweak angle ismeasured. The electronmasscannotbepredicted ( thecouplingconstant g isunknown ).

  29. problem: mass generation electroweak theory: mass generation by SSB QCD: mass generation by confinement

  30. hypotheticalHiggsboson

  31. limit on mass of Higgs boson from LEP: 114 GeV

  32. L3 Alice CMS ATLAS I LHCb LEP - LHC

  33. muon H===> Z Z LHC Higgs particle

  34. - other possibility to generate the masses for the weak bosons: W =>pion=>W pion W W M(W)~100 MeV

  35. - technicolor W =>technipion=>W technipion W W M(W)~100 GeV

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